Handheld electric machine tool

ABSTRACT

A handheld electric machine tool is described including a housing with a grip area, a tool area for a tool that is drivable in a linear and/or oscillating manner, an operating part on the housing for activation of the tool and/or the electric machine tool by the user, a drive unit disposed in the housing for producing a working motion of the tool, an electronic unit disposed in the housing for acting upon the drive unit with at least control and/or regulating signals, an operating voltage unit for supplying an electrical DC voltage, the drive unit including at least one excitation actuator having a volume of excitation-active material, which excitation actuator when in operation is electrically supplied by the operating voltage unit, is controlled or regulated by the electronic unit. The electronic unit may be configured to operate the at least one excitation actuator in a resonant frequency.

FIELD OF THE INVENTION

The present invention relates to a handheld electric machine toolincluding a housing with a grip area, a tool area for a tool that isdrivable in a linear and/or rotary oscillating manner, an operating parton the housing for activation of the tool and/or the electric machinetool by the user, a drive unit disposed in the housing for producing aworking motion of the tool, an electronic unit disposed in the housingfor acting upon the drive unit with the required machining outputconsisting of at least control and/or regulating signals, an operatingvoltage unit for supplying an electrical DC voltage to the electronicunit, the drive unit including at least one excitation actuator having avolume of excitation-active material, which excitation actuator when inoperation is electrically supplied by the operating voltage unit and iscontrolled or regulated by the electronic unit.

BACKGROUND INFORMATION

Handheld electric machine tools are characterized by being portable andby being held and guided by a user by hand when in operation. They maybe cordlessly operated by battery packs or may be operated with mainscurrent. In particular, they generally consist of only one housing whichis completely held by the user.

European Patent No. EP 1 598 171 B1 describes a mechanical configurationof a welding head of a portable welding gun in which an ultrasoundactuator acts upon the welding head with mechanical power.

SUMMARY

The present invention relates to a handheld electric machine toolincluding a housing with a grip area, a tool area for a tool that isdrivable in a linear and/or rotary oscillating manner, an operating parton the housing for activation of the tool and/or the electric machinetool by the user, a drive unit disposed in the housing for producing aworking motion of the tool, an electronic unit disposed in the housingfor acting upon the drive unit with the required machining outputconsisting of at least control and/or regulating signals, an operatingvoltage unit for supplying an electrical DC voltage to the electronicunit, the drive unit including at least one excitation actuator having avolume of excitation-active material, which excitation actuator when inoperation is electrically supplied by the operating voltage unit and iscontrolled or regulated by the electronic unit.

The electronic unit is configured to operate the at least one excitationactuator in a resonant frequency.

If the excitation actuator is operated with its resonant frequency, itis possible, with a sufficiently high Q factor of the oscillatingsystem, for a high mechanical output power to be delivered correspondingto an electrical input power. The excitation actuator may be anultrasound excitation generator, especially a piezo actuator in thestyle of a Langevin oscillator. The piezo actuator has excitation-activematerial as the piezoelectric material. Typically, the Q factor of theundamped oscillating system lies at values above 100, typically above500. The resonance system of the excitation actuator, which has theresonant frequency, includes the Langevin oscillator withpiezoelectrically active material, and components coupled to theoscillator, especially components that amplify the ultrasound and/ortransmit it to a machining site. Such components are known, for example,as boosters or sonotrodes. This makes possible a reduction in overallsize and makes it possible to provide a compact device. Thatadvantageously produces a compact, high-performance electric machinetool which is handy at the same time.

It is also possible for a plurality of excitation actuators, for exampleof the same or also of differing resonant frequency, to be provided asdrive components. Alternatively, it is also possible for one or morefurther drive components, such as an electric motor, to be provided. Thevarious drive components may be operated as alternatives or incombination. If the at least one excitation actuator is operated inresonance, the power yield is particularly high, so that, for a givenoutput power of the electric machine tool, the construction may beparticularly compact, which is also conducive to comfortable handling ofthe handheld electric machine tool. The proposed electric machine toolis a one-piece implement with which it is possible to dispense withtroublesome connection cables between separate housing parts. Theelectric machine tool may be operable cordlessly with non-rechargeableor rechargeable batteries or—in addition or alternatively—may beoperable by mains power via a mains cable. The tool may be aninterchangeable tool detachably connected to the excitation actuator orit may be fixedly connected to the excitation actuator. The connectionmay, for example, be integral or non-positive. The electric machine toolis especially a machining tool with which objects or surfaces may bemachined or modified, such as, for example, drills, hammer drills,cutting tools, grinding machines, milling machines, saws, weldingdevices and the like.

In accordance with an advantageous development of the present invention,the electronic unit may include a regulating unit with frequencymatching for adjustment of the resonant frequency of the at least oneexcitation actuator. Advantageously, during operation of the electricmachine tool the resonant frequency may be continuously adapted if, forexample, the resonant frequency of the excitation actuator changes dueto temperature change, changing of the tool coupled to the excitationactuator or upon loading of the tool. In that manner, an optimum poweryield is always made possible in operation. Advantageously, theelectronic unit may include a phase-regulating chain with which theresonant frequency may be excited with high accuracy. In that manner, aphase shift between the electrical current and electrical voltagesupplied to the piezoelectrically active material to excite theultrasonic oscillations may be set and maintained at a fixed value,especially 0° phase difference between current and voltage signal,thereby enabling an optimum power yield to be achieved.

In accordance with an advantageous development of the present invention,the volume of the piezoelectrically active material may be at least 0.2cm³, preferably 0.5 cm³, especially at least 1 cm³. Advantageously, itis possible for a sufficient ultrasound power to be achieved with asmall overall size of the excitation actuator.

In accordance with an advantageous development of the present invention,the at least one excitation actuator may have a power density of atleast 5 Watt/cm³, preferably at least 20 Watt/cm³, based on the volumeof the piezo-electrically active material of the at least one excitationactuator. A correspondingly high power density is advantageous for ahandheld compact electric machine tool having the smallest possibledimensions and low production costs.

In accordance with an advantageous development, the at least oneexcitation actuator may have, at the tip of the tool, an oscillationamplitude of at least 3 μm, preferably at least 8 μm, especially atleast 12 μm. A correspondingly high oscillation amplitude isadvantageous for good power transfer to the workpiece and hence for ahigh rate of work progress by the electric machine tool.

In accordance with an advantageous development of the present invention,on the input side of the electronic unit an electrical power for actingupon the at least one excitation actuator may be at least 20 Watt.Advantageously, it is thereby possible to ensure sufficient power for anelectric machine tool. Customary power outputs in the do-it-yourselfsector are, for small cutting systems, approximately from 20 Watt to 250Watt, preferably from 50 Watt to 150 Watt. For higher-poweredapplications, for example drilling, power outputs starting at 50 Watt upto 1000 Watt, preferably from 200 Watt to 500 Watt, are required. In theprofessional trade sector, the power requirement for small systems isapproximately from 50 to 400 Watt, preferably from 100 to 250 Watt. Inthe case of large systems, power outputs of from 200 Watt to 2000 Watt,preferably from 400 Watt to 1000 Watt, are employed. It is neverthelesspossible to produce an electric machine tool with handy dimensions whichnot only is capable of being gripped or held by the hand of the user butalso affords a sufficiently high power output for machining purposes.

In accordance with an advantageous development of the present invention,a maximum electric excitation field strength of the at least oneexcitation actuator may be in the range below 300 V/mm (based on thethickness, especially disc thickness, of the piezoelectrically activematerial), preferably in the range from 50 V/mm to 220 V/mm. At a discthickness of the excitation actuator of typically from 1 mm to 10 mm,preferably from 2 mm to 6 mm, and especially of around 5 mm, theelectrical voltages are below 1000 Volt. That advantageously makes itpossible for the excitation actuator to be used in the handheld electricmachine tool with sufficient mechanical output power while havingadvantageously small dimensions.

In accordance with an advantageous development of the present invention,an electrical output voltage of the operating voltage unit when suppliedby electrochemical storage devices may be within from 3 Volt to 100 VoltDC, preferably in the range from 3.5 V to 40 V, and especially may be 36Volt, 24 Volt, 18 Volt, 14.4 Volt, 12 Volt, 10.6 Volt, 7.2 Volt and 3.6Volt. It is advantageously possible to use non-rechargeable batterypacks or rechargeable battery packs that are small and light enough tostill afford easy handling of the electric machine tool at high poweroutput.

In accordance with an advantageous development of the present invention,a DC voltage component of the electrical output voltage of the operatingvoltage unit when supplied with mains voltage may be within from 0.5U_(mains) (effective value of mains voltage) to 2 U_(mains). Preferably,for example with the use of a bridge rectifier with smoothing capacitor,1.4 U_(mains). In a further embodiment, the mains voltage may betransformed using an input-side transformer to a voltage suitable forthe operating voltage unit.

In accordance with an advantageous development of the present invention,the operating frequency of the at least one excitation actuator may bein the range of from 10 kHz to 1000 kHz, preferably from 30 kHz to 50kHz, and especially from 35 kHz to 45 kHz, more especially around 40kHz. With increasing frequency, the overall size of the componentsdecreases and the mechanical load on the oscillating system increases,producing in the selected frequency range advantageous proportions withhigh output power and favorable weight of the electric machine tool.

In accordance with an advantageous development of the present invention,the operating voltage unit may include an electrochemical storagedevice, preferably a rechargeable electrochemical storage device. Theoperating voltage unit takes up only very little space, which isadvantageous in terms of the compactness and weight of the electricmachine tool. Advantageous systems are those based on, for example,lithium ions (Li ions) or also nickel-metal hydride (NiMeH),nickel-cadmium (NiCd) or also lead and the like. These may be fixedlyintegrated in the housing and recharged via a charging connection.Alternatively, the operating voltage unit may be in the form of anexchangeable system, with replaceable electrochemical storage deviceswhich may also be rechargeable externally if appropriate and which maybe plugged into a holder provided for the purpose in or on the housing.Depending on the power output required, the rated voltage of theoperating voltage unit may be, for example, from 3 Volt DC to 48 VoltDC, for example 12 Volt DC.

In accordance with an advantageous development of the present invention,the operating voltage unit may include an AC/DC transformer unit. Inthat case, a mains connection may also be provided for the electricmachine tool, and rectification and smoothing of the mains voltage maytake place in the operating voltage unit. Although the conditioning ofthe mains voltage requires more space than an energy storage device, thefurther space-saving and compact construction in a single housing stillmakes simplified operation and handling of the electric machine toolpossible.

In accordance with an advantageous development of the present invention,the electronic unit may be concentrated on a printed circuit board. Thatallows a particularly space-saving arrangement in the housing. Theelectronic activation system of the excitation actuator is particularlycompact.

In accordance with an advantageous development of the present invention,for signal filtering and for inductive compensation of the at least oneexcitation actuator at least one inductance may be provided in a powercircuit of the electronic unit acting upon the at least one excitationactuator with electrical power. It is possible to achieve a space-savinglayout of the power inductances in a single coil core. The signalfiltering and inductive compensation of the piezo actuator, which isbeneficial in the case of excitation actuators, may be provided directlyby a specifically adjusted stray inductance of a transmissiontransformer that is required in any case, or may be afforded by aninductance wound on the same coil core. An additional coil core with afurther inductance in the power circuit may thereby be omitted.

In accordance with an advantageous development of the present invention,at least drive unit, electronic unit and operating voltage unit may bedistributed in the housing in such a manner that a center of gravitylies in the region of the grip part. The user is able to handle theelectric machine tool safely and conveniently. Safety and ease of useare enhanced.

In accordance with an advantageous development of the present invention,the drive unit may include, in addition to the at least one excitationactuator, at least one further drive component. Advantageously, a motionproduced by the at least one excitation actuator may be superimposed onthe working motion of a tool driven by the at least one further drivecomponent, thereby enabling work progress to be considerably improvedand making the machining easier.

In accordance with an advantageous development of the present invention,the at least one excitation actuator may form a main energy consumer ofthe electric machine tool, for which preferably at least 50% of theelectrical input power may be provided. In an advantageous development,at least 75%, preferably at least 80%, of the electrical input power maybe provided for the excitation actuator. The rate of work progress ofthe electric machine tool when using ultrasound is especially high, andtherefore a further energy consumer, especially a further drivecomponent, such as a drill, chisel, cutter or the like, may be smaller.That means that the drive and associated electronic components and theenergy supply may also be smaller, which in turn allows enhanced ease ofuse and improved handling of the handheld electric machine tool.

In accordance with an advantageous development of the present invention,one or more operating indicators for an activated state of the at leastone excitation actuator may be provided. The indicators may be opticaland/or acoustic and/or haptic. The operating safety of the electricmachine tool is increased, since it is clearly evident when theexcitation actuator is activated and capable of delivering mechanicalpower.

In accordance with an advantageous development of the present invention,the drive unit which imparts a working motion to the tool may impartsuperimposed oscillations to the tool. The drive unit may have as afurther drive component, for example, an electric drive motor which ishoused in the housing of the electric machine tool. The motor shaft isnormally coupled via a gear unit to a tool shaft which is the carrier ofthe tool and executes the working motion. The tool is usually to befastened to the tool shaft in an interchangeable manner.

The electric machine tool may, for example, be used for chip-generatingmachining of workpieces, where, to reduce the chip size, the excitationactuator, which is able to produce superimposed oscillations in thetool, is advantageously disposed in the electric machine tool. Thosesuperimposed oscillations are superimposed on the working motion of thetool.

According to the type of electric machine tool and depending on the toolused and the material of the workpiece to be machined, the superimposedoscillations, which emanate not from the drive motor but from theexcitation actuator, may be generated with a frequency that results in asignificant reduction in the chip size. Since smaller chips also have asmaller heat capacity, the chips are able to cool down in a shortertime, thereby reducing the fire risk. Furthermore, the smaller chips perse lead to a reduced risk of injury, since their momentum is lower.

The frequency of the superimposed oscillations is expediently in theultrasound range and may thus be, for example, at least 20 kHz. Thatcomparatively high frequency has, on the one hand, the advantage thatoscillations in that order of magnitude are no longer audible to humans,and therefore no noise nuisance occurs. On the other hand, it has beenfound that oscillations at and above that order of magnitude areparticularly effective in significantly reducing the size of the chipsproduced in the machining of a workpiece.

It may be expedient to generate superimposed oscillations that are inconsiderably greater orders of magnitude. In principle, oscillations upto and including the megahertz range come into consideration. Inaddition, it is also possible to generate superimposed oscillations oflower frequency.

Owing to the superimposition on the working motion of the tool, on theone hand, and owing to the generally distinctly higher frequency, thegeneration of the superimposed oscillations has no effect on the workingmotion and hence on the result of the workpiece machining operation. Inaddition, the superimposed oscillations are usually of only a very smallamplitude, so that the machining of the workpiece is not impaired.

The advantageous generation of superimposed oscillations in the tool maybe used both in rotary and in translational or in a mixture of rotaryand translational working motions of the tool. In accordance with anadvantageous embodiment, the electric machine tool is in the form of agrinding device, for example an angle grinder, having as the tool agrinding wheel supported on a tool shaft, the motion of the tool beingexclusively a rotary motion in that case. There also come intoconsideration, however, translational motions, for example in the caseof hacksaws which execute an oscillatory stroke movement.

The superimposed oscillations may, in accordance with an advantageousembodiment, be excited orthogonally to the plane of motion of the toolin which the working motion takes place. For example, in the case ofgrinding wheels, the superimposed oscillations may be applied in thedirection of the tool shaft carrying the grinding wheel. In the case ofa translational working motion, on the other hand, the superimposedoscillation takes place perpendicularly to the translational motion.

In accordance with a further advantageous embodiment, it is alsopossible, however, for the superimposed oscillations to excite the toolin the plane of motion. In the case of a grinding wheel, this means thatthe grinding wheel is excited perpendicularly to the tool shaft, so thatthe vector of the excitation lies in the plane of motion of the grindingwheel.

It may furthermore be advantageous to cause the superimposedoscillations emanating from the excitation actuator to act upon abearing of the tool, in which case the oscillations also propagate viathe bearing to the tool. In the case of a plurality of bearings, this ispreferably done via the bearing that is near the tool in order to avoidloading of the gear unit and the drive motor by the superimposedoscillations.

As excitation actuator, it is possible to use active actuators ofvarious configurations capable of being excited by supply of energy togenerate oscillations. In accordance with an advantageous embodiment, itmay be provided that the excitation actuator is in the form of aLangevin oscillator, with piezo elements clamped therein, which changesits dimensions as a result of application of a voltage. As a result ofbeing acted upon by an appropriately high-frequency voltage, the piezoelement is able to expand and contract in the desired frequency of thesuperimposed oscillations, the excitation actuator being coupled to acomponent in the force transmission chain between drive unit or drivemotor and tool so that the oscillations of the excitation actuator maypropagate into the tool. As already described previously, the excitationis preferably effected by way of a bearing of the tool shaft carryingthe tool. In accordance with an advantageous embodiment, it is providedthat the excitation actuator is in the form of a magneto-restrictiveexcitation actuator, which is especially suitable for generatingultrasonic oscillations.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages will be apparent from the following description ofthe figures. Exemplary embodiments of the present invention areillustrated in the figures. The figures and the description containnumerous features in combination. The person skilled in the art willadvantageously also consider the features individually and combine themto make sensible further combinations.

FIG. 1 shows an exemplary embodiment of a handheld electric machine toolconfigured as a cutting tool.

FIG. 2 shows a further exemplary embodiment of a handheld electricmachine tool configured as a drill.

FIG. 3 a, 3 b show an outline sketch of an activation assembly with anAC voltage power supply by mains current or with a DC voltage powersupply by a battery pack (FIG. 3 a) and an advantageous clocking forreducing the overall size of a filter unit (FIG. 3 b).

FIG. 4 shows a progression of an ultrasound amplitude along a sonotrode.

FIG. 5 shows an impedance characteristic for detecting a resonantfrequency of an excitation actuator.

FIG. 6 shows an equivalent circuit diagram of an ideal transformer.

FIG. 7 is a sectional view of an electric machine tool in the form of anangle grinder.

FIG. 8 is a detailed view of the grinding wheel of the angle grinder ofFIG. 7, disposed on a tool shaft, the tool shaft being received inbearings and the bearing near the tool being acted upon withhigh-frequency oscillations transversely to the shaft axis by anexcitation actuator.

FIG. 9 shows the grinding wheel of FIG. 8 with bearing and excitationactuator in plan view.

FIG. 10 shows a further exemplary embodiment, in which the excitationactuator acts upon the tool shaft carrying the grinding wheel withhigh-frequency oscillations in the axial longitudinal direction.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In the Figures, components that are identical or of the same kind arenumbered with identical reference numerals.

To explain the present invention, FIGS. 1 and 2 show different examplesof handheld electric machine tools 10. FIG. 1 shows a cutting tool withelongate housing shape; FIG. 2 shows a drill with T-form housing shape.

Handheld electric machine tool 10 includes a housing 20 with a grip area40. A user holds electric machine tool 10 at the grip area 40 and isable to guide electric machine tool 10. Grip area 40 may, whereappropriate, be decoupled from other areas of the housing by a dampingelement, not shown. Electric machine tool 10 further includes a toolarea 50 for a tool 60 which is drivable in a linear and/or oscillatingmanner, for example a cutter (FIG. 1) or a drill (FIG. 2) or anothertool corresponding to another type of device.

An operating part 30 on the housing is used for activation of tool 60and/or electric machine tool 10 by the user. Operating part 30 may, forexample, be a switch or a controller or may also include a plurality ofoperating elements, one of which may be provided, for example, forswitching on electric machine tool 10 and one of which may be providedfor switching on and/or controlling tool 60.

Arranged in housing 20 there is a drive unit 80 which, in the examplesshown in FIG. 1 and FIG. 2, includes only one drive component which isformed by an excitation actuator 100. The latter may be in the form of apiezo-excited Langevin oscillator (also called a piezo actuator) whichincludes a volume of piezoelectrically active material 102, for examplepiezo-ceramic discs which are pressed together and which undergo achange in length when acted upon by electrical voltage. Whenhigh-frequency electrical voltage is applied, in a conventional mannerultrasound is generated which is passed via a coupling element 106 to atool 60. Coupling element 106 may be a conventional sonotrode. Thelength and shape and also the material of coupling element 106 determinea resonant frequency of excitation actuator 100. Tool 60 may also havean influence on the resonant frequency. In the embodiment variants inFIG. 1 and FIG. 2, excitation actuator 100 is configured in such a waythat Langevin oscillator and coupling element 106 are combined in aunit, and the total length thereof approximately corresponds to half thewavelength λ/2 of the ultrasonic oscillation. Other embodiment variantsmay provide that excitation actuator 100 is composed of a plurality ofcomponents of length λ/2. These may be: oscillation generators, known asconverters, specifically, for example, a Langevin oscillator, amplitudetransformation pieces 104, known as boosters, where applicablelengthening pieces, and coupling element 106 known as a sonotrode.

An electronic unit 200 arranged in housing 20 serves to apply at leastcontrol and/or regulating signals to drive unit 80 and to supply voltageto excitation actuator 100. An operating voltage unit 90, in the form ofa non-rechargeable or rechargeable battery pack with non-rechargeable orrechargeable batteries 92 here, serves to provide an electrical DCvoltage for electronic unit 90 which converts the operating voltage intoa high-frequency voltage signal with which excitation actuator 100 isexcited into oscillation in the desired manner.

Electronic unit 200 is configured to operate the at least one excitationactuator 100 in a resonant frequency f_res. Electronic unit 200 includesa regulating unit 224 for re adjustment of the resonant frequency f_resof excitation actuator 100. Regulating unit 224 may include a phaseregulating chain capable of exciting excitation actuator 100 into itsresonant frequency, with a phase shift between incoming current andincoming voltage being set to 0°. Preferably, resonant frequency f_resis regulated accordingly if the resonant frequency changes owing toheating or changing load at the tool. Alternatively, frequencyre-adjustment may also be carried out by regulating to a maximum of thecurrent fed into excitation actuator 100.

If excitation actuator 100 is a piezo actuator, the volume ofpiezoelectrically active material 102, for example stacked piezoelectricdiscs, is advantageously at least 0.2 cm³, preferably 0.5 cm³,especially at least 1 cm³. Excitation actuator 100 may have a powerdensity of at least 5 Watt/cm³, preferably at least 20 Watt/cm³, basedon the volume of piezoelectrically active material 102 of excitationactuator 100. The power density makes use possible in a handheldelectric machine tool 10 with sufficient power delivery of tool 60.

Activation of tool 60 by activation actuator 30 may be indicated by asignal element 122 (FIG. 2).

In FIG. 1, electronic unit 200 is integrated in a particularlyspace-saving manner on a single printed circuit board 210. In FIG. 2,the electronic unit is divided between two printed circuit boards 212,214, one being disposed in the main part and one being disposed in thegrip part of T shaped housing 20, which grip part juts out at rightangles to the main part. Advantageously, drive unit 80, electronic unit200 and operating voltage unit 90 are distributed in housing 20 in sucha way that a center of gravity lies in the region of grip part 40.

FIG. 3 a shows an outline sketch of an activation of excitation actuator100, for example in the form of piezo actuator 100, with an AC voltagepower supply from a mains supply network or with a DC voltage powersupply with a battery pack.

When electronic unit 200 has a mains power supply, for example 220 VoltAC, a component assembly 94 is provided that rectifies and smoothes theAC voltage. Electronic unit 200 includes a power generating unit 222into which the DC voltage is fed and which is coupled to excitationactuator 100 via a suitable filter unit 226. A regulating unit 224provides the regulating signals for excitation actuator 100. Theoperating frequency of excitation actuator 100 is in the range of from10 kHz to 1000 kHz, preferably from 30 kHz to 50 kHz, and especiallyfrom 35 kHz to 45 kHz, more especially around 40 kHz.

If power is supplied by operating voltage unit 90 using non-rechargeableor rechargeable batteries 92, it is possible to reduce the spacerequired, since it is possible to omit component assembly 94 forrectifying and smoothing. The electrical output voltage of operatingvoltage unit 90 is preferably below 100 Volt, and is approximately 36Volt or 10.8 Volt.

The maximum electric excitation field strength of the at least oneexcitation actuator is preferably in the range below 300 V/mm (based onthe thickness, especially disc thickness, of the piezoelectricallyactive material), preferably in the range of from 50 V/mm to 220 V/mm.At a disc thickness of excitation actuator 100 of typically from 1 mm to10 mm, preferably 2 mm to 6 mm, and especially of around 5 mm, theelectrical voltages are below 1000 Volt.

In one embodiment variant, power generating unit 222 may be implementedby 4 MOSFET semiconductors in a conventional full bridge topology. In afurther variant, the generation of the operating signal may also beeffected by a conventional half bridge topology with, for example, a midpoint capacitor for filtering the DC component.

FIG. 3 b illustrates one possibility for making the overall size offilter unit 226 as small as possible. For that purpose, power unit 222may be driven by regulating unit 224 in such a manner that, bysine-triangle modulation for example, it generates instead of simplesquare-wave signals a square-wave voltage that is more similar to asine. Depending on the level of the clocking, that is, the number ofindividual pulses that together reproduce a sine, the content ofundesirable harmonics may be distinctly reduced, which results in asmaller design of filter unit 226. For this, the number of square-wavepulses per cycle duration of the sinusoidal signal is greater than 6,preferably in the range of from 6 to 100, especially in the range offrom 10 to 26. In one embodiment variant, the number and width of thesquare-wave pulses of regulating unit 224 may also be varied duringoperation, for example with changes in load.

FIG. 4 shows a progression of an ultrasound amplitude along anexcitation actuator 100 in the form of a piezo actuator. Couplingelement 106 is in the form of a sonotrode. The region of excitationactuator 100 adjoining piezoelectric material 102 is referred totogether with piezo discs 102 as a converter. Piezoelectric material 102is excited by the supplied high-frequency AC voltage into oscillationswhich are transmitted into coupling element 102 via the converter. Inthe case of a three-stage structure of excitation actuator 100 such asthat shown in FIG. 4, excitation actuator 100 additionally consists of abooster 104 for amplitude matching. Along the length M of excitationactuator 100 the amplitude Amp of the excited oscillation increases onaverage. Variations in the resonant frequency f_res of the oscillatingsystem of excitation actuator 100 (where applicable with attached tool)during operation are preferably compensated for, for example using aphase regulating chain already described above with which the phaseshift between the electrical voltage fed into excitation actuator 100for excitation thereof and the electrical current fed in is regulated tozero (phase zero regulation), or using a maximum regulation of theelectrical current fed into excitation actuator 100.

FIG. 5 shows an impedance characteristic of an excitation actuatorimplemented by a piezo actuator with the resonant frequencies f_res andf_res2. Curve A shows the variation of the impedance Imp as a functionof the frequency f, which passes through an impedance minimum atresonant frequency f_res and through an impedance maximum at f_res2. Thefrequency f_res is referred to as series resonance, and f_res2 asparallel resonance.

Curve B shows the variation of the phase shift between current andvoltage, which has a zero crossing at the resonant frequency and changesfrom −90° below the resonant frequency f_res to +90° above the resonantfrequency f_res. On passing through the parallel resonance f_res2, thephase shift changes from +90° below the resonant frequency to −90° abovethe resonant frequency.

For signal filtering and for inductive compensation of the at least oneexcitation actuator 100, at least one inductance may be provided in apower circuit of the electronic unit, which circuit acts upon the atleast one excitation actuator 100 with electrical power. It is possibleto obtain a space-saving layout of the power inductances together withthe transmission transformer in a single coil core. The signal filteringand inductive compensation of the piezo actuator, which is beneficial inthe case of excitation actuators 100, may be provided directly by aspecifically adjusted stray inductance of a transmission transformerthat is required in any case, or may be afforded by an inductance woundon the same coil core. An additional coil core with a further inductancein the power circuit may thereby be omitted.

To illustrate this, FIG. 6 shows an equivalent circuit diagram with anideal transformer. The inductance M is used for the actual transfer fromprimary side to secondary side. The stray inductances occur since it isnever possible for the windings to be ideally coupled. L1 and L2 formthe part of the magnetic field that cannot be “captured” by thesecondary coil. L1 and L2 are to be regarded in electrical terms asbeing like an air-core coil.

Electric machine tool 10 shown as an angle grinder in FIG. 7 includes ahousing 20 consisting of a motor housing 22 and a grip housing 24, adamping element 26 being disposed between motor housing 22 and griphousing 24. Electric machine tool 10 is held at grip housing 24 whichforms grip area 40. Motor housing 22 houses a drive unit 80 with a drivecomponent in the form of an electric drive motor 82 which is coupled toand drives a tool shaft 64 via a gear unit 62. Tool shaft 64 is thecarrier for a tool 60, in the form of a grinding wheel, which isfastened interchangeably to tool shaft 64.

In FIG. 8, tool shaft 64 and tool 60 fastened thereto in the form of agrinding wheel are shown in a detail view. Tool shaft 64, which haslongitudinal axis L, is rotatably supported in bearings 70 and 72 spacedapart from each other in housing 20. Situated on tool shaft 64 at theopposite end face from the grinding wheel, there is a beveled wheel 74via which tool shaft 64 is driven by electrical drive motor 82.

To reduce the size of the chips produced during machining of a workpiecewith tool 60 in the form of a grinding wheel, tool 60 in the form of agrinding wheel is set into high-frequency oscillation in addition to itsrotary working motion. This involves superimposed oscillations which aresuperimposed on the working motion of tool 60 in the form of a grindingwheel. Those superimposed oscillations are generated with the aid ofexcitation actuator 100 which is also disposed in housing 10 of handheldelectric machine tool 10 as a further drive component of drive unit 80and which directly or indirectly excites tool 60 in the form of agrinding wheel into the superimposed oscillations. In the exemplaryembodiment shown in FIG. 8, excitation actuator 100 acts upon tool-sidebearing 70 of tool shaft 64 and generates superimposed oscillations thatare directed orthogonally to longitudinal axis L of tool shaft 64. Thosesuperimposed oscillations directed orthogonally to longitudinal axis Lare also transmitted via tool shaft 64 to tool 60 in the form of agrinding wheel which similarly executes superimposed oscillationsorthogonally to longitudinal axis L and thus in its plane of motion.

It is also possible for excitation actuator 100 to be positioned at adifferent location, for example at bearing 72 remote from the tool ordirectly at a position on tool shaft 64 or on tool 60 in the form of agrinding wheel in order for tool 60 to be acted upon directly bysuperimposed oscillations.

Various active actuators may be used as excitation actuator 100.Preference is given to the use of actuators that generate high-frequencyoscillations in the ultrasound range, especially in a frequency range ofat least 20 kHz, but with frequencies in higher orders of magnitudecoming into consideration, especially up to and including the megahertzrange, or also smaller frequencies.

By way of example, there is used as excitation actuator 100 a piezoelement whose length changes as a result of application of an electricalvoltage. Since piezo elements respond very rapidly to voltage changes,by applying a high-frequency voltage it is possible to produce acorrespondingly rapid change in length in the excitation actuator, whichexerts an effect on tool 60 which by way of example is in the form of agrinding wheel here.

Excitation actuator 100 may also be in the form of a magneto-resistiveactuator in which the electrical resistance is changed by application ofan external magnetic field.

In the exemplary embodiment shown in FIGS. 8 and 9, the superimposedoscillations are generated in the direction of arrow 110, orthogonallyto longitudinal axis L of tool shaft 64 and tool 60 in the form of agrinding wheel. In the exemplary embodiment shown in FIG. 10, on theother hand, excitation with the superimposed oscillations takes place inaccordance with arrow direction 110, in the direction of longitudinalaxis L of tool shaft 64 and tool 60 and thus perpendicularly to theplane of motion of tool 60 in the form of a grinding wheel. Excitationactuator 100, by which the superimposed oscillations are generated, actseither directly upon tool shaft 64 or one or both bearings 70 and 72 ordirectly upon tool 60 with the superimposed oscillations in the axialdirection.

1-28. (canceled)
 29. A handheld electric machine tool, comprising: ahousing with a grip area; a tool area for a tool that is drivable in atleast one of a linear and oscillating manner; an operating part on thehousing for activation by a user of at least one of the tool and theelectric machine tool; a drive unit disposed in the housing to produce aworking motion of the tool; an electronic unit disposed in the housingto act upon the drive unit with at least one of control signals andregulating signals; and an operating voltage unit to supply anelectrical DC voltage, wherein the drive unit includes at least oneexcitation actuator having a volume of excitation-active material, whichexcitation actuator when in operation is electrically supplied by theoperating voltage unit, is controlled or regulated by the electronicunit; wherein the electronic unit is configured to operate the at leastone excitation actuator in a resonant frequency.
 30. The handheldelectric machine tool as recited in claim 29, wherein the electronicunit includes a regulating unit with frequency matching for readjustment of the resonant frequency of the at least one excitationactuator.
 31. The handheld electric machine tool as recited in claim 29,wherein the excitation-active material is piezoelectric.
 32. Thehandheld electric machine tool as recited in claim 31, wherein a volumeof the piezoelectric material is at least 0.2 cm³.
 33. The handheldelectric machine tool as recited in claim 31 wherein a volume of thepiezoelectric material is at least 0.5 cm³.
 34. The handheld electricmachine tool as recited in claim 31 wherein a volume of thepiezoelectric material is at least 1 cm³.
 35. The handheld electricmachine tool as recited in claim 32, wherein the at least one excitationactuator has a power density of at least 5 Watt/cm³, based on the volumeof the piezoelectrically active material of the at least one excitationactuator.
 36. The handheld electric machine tool as recited in claim 35wherein the power density is at least 20 Watt/cm³.
 37. The handheldelectric machine tool as recited in claim 29, wherein the at least oneexcitation actuator has, at a tip of the tool, an oscillation amplitudeof at least 3 μm.
 38. The handheld electric machine tool as recited inclaim 37, wherein the oscillation amplitude is at least 8 μm.
 39. Thehandheld electric machine tool as recited in claim 37, wherein theoscillation amplitude is at least 12 μm.
 40. The handheld electricmachine tool as recited in claim 29, wherein on an input side of theelectronic unit, an electrical power for acting upon the at least oneexcitation actuator is at least 20 Watt.
 41. The handheld electricmachine tool as recited in claim 29, wherein a disc thickness of theexcitation actuator is from 1 mm to 10 mm.
 42. The handheld electricmachine tool as recited in claim 41, wherein the disc thickness isbetween 2 mm to 6 mm.
 43. The handheld electric machine tool as recitedin claim 41, wherein the disc thickness is 5 mm.
 44. The handheldelectric machine tool as recited in claim 31, wherein an input fieldstrength of the at least one excitation actuator is in the range below300 V/mm, based on a thickness of the piezoelectrically active material.45. The handheld electric machine tool as recited in claim 44, whereinthe range is from 50 V/mm to 220 V/mm.
 46. The handheld electric machinetool as recited in claim 29, wherein an input voltage of the at leastone excitation actuator is in a range below 1000 Volts.
 47. The handheldelectric machine tool as recited in claim 46, wherein the range is from300 Volts to 700 Volts.
 48. The handheld electric machine tool asrecited in claim 29, wherein an electrical output voltage of theoperating voltage unit is below 100 Volts.
 49. The handheld electricmachine tool as recited in claim 29, wherein an electrical outputvoltage of the operating voltage unit is above 100 Volts.
 50. Thehandheld electric machine tool as recited in claim 29, wherein anoperating frequency of the at least one excitation actuator is in therange of from 10 kHz to 1000 kHz.
 51. The handheld electric machine toolas recited in claim 50, wherein the range is from 30 kHz to 50 kHz. 52.The handheld electric machine tool as recited in claim 50, wherein therange is from 35 kHz to 45 kHz.
 53. The handheld electric machine toolas recited in claim 29, wherein the operating voltage unit includes anelectrochemical storage device.
 54. The handheld electric machine toolas recited in claim 53, wherein the electrochemical storage device isrechargeable.
 55. The handheld electric machine tool as recited in claim29, wherein the operating voltage unit includes a rectifier.
 56. Thehandheld electric machine tool as recited in claim 29, wherein theelectronic unit is concentrated on a printed circuit board.
 57. Thehandheld electric machine tool as recited in claim 29, wherein theelectronic unit includes at least one inductance provided in a powercircuit acting upon the at least one excitation actuator with electricalpower for at least one of signal filtering and inductive compensation ofthe at least one excitation actuator.
 58. The handheld electric machinetool as recited in claim 29, wherein at least the drive unit, theelectronic unit and the operating voltage unit are distributed in thehousing in such a manner that a center of gravity lies in a region ofthe grip part.
 59. The handheld electric machine tool as recited inclaim 29, wherein the drive unit further includes at least one furtherdrive component.
 60. The handheld electric machine tool as recited inclaim 29, wherein the at least one excitation actuator forms a mainenergy consumer of the electric machine tool, for which at least 50% ofthe electrical input power is provided.
 61. The handheld electricmachine tool as recited in claim 29, further comprising: at least one ofan optical, acoustic, and haptic operating indicator to indicate anactivated state of the at least one excitation actuator.
 62. Thehandheld electric machine tool as recited in claim 29, furthercomprising: an illumination element for a working area.
 63. The handheldelectric machine tool as recited in claim 29, wherein the excitationactuator is configured to generate superimposed oscillations in the toolwhich are superimposed on a working motion of the tool.
 64. The handheldelectric machine tool as recited in claim 29, wherein the tool isrotatably supported and a working motion of the tool is a rotationalmotion.
 65. The handheld electric machine tool as recited in claim 64,wherein the tool is a grinding wheel.
 66. The handheld electric machinetool as recited in claim 63, wherein the superimposed oscillationsexcite the tool in at least one of (i) orthogonally to a plane of motionof the tool in which the working motion of the tool takes place, (ii) ina direction of the longitudinal axis of a tool shaft carrying the tool,(iii) in a plane of motion in which the working motion of the tool takesplace, and (iv) perpendicularly to the tool shaft.
 67. The handheldelectric machine tool as recited in claim 29, wherein the excitationactuator acts upon a bearing of the tool.
 68. The handheld electricmachine tool as recited in claim 29, wherein an excitation-activematerial of the excitation actuator is magneto-restrictive.